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In choose-by-bw, scale to better use the range of uint64

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The smart part of this is based on an approach and a suggestion by
rransom. The unsmart part is my own fault.
This commit is contained in:
Nick Mathewson 2012-08-27 17:37:56 -04:00
parent ef628649c8
commit 5c3199cda7
3 changed files with 131 additions and 51 deletions
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109
src/or/routerlist.c
View File

@ -1653,15 +1653,41 @@ router_get_advertised_bandwidth_capped(const routerinfo_t *router)
return result;
}
/** Given an array of double/uint64_t unions that are currently being used as
* doubles, convert them to uint64_t, and try to scale them linearly so as to
* much of the range of uint64_t. If <b>total_out</b> is provided, set it to
* the sum of all elements in the array _before_ scaling. */
/* private */ void
scale_array_elements_to_u64(u64_dbl_t *entries, int n_entries,
uint64_t *total_out)
{
double total = 0.0;
double scale_factor;
int i;
/* big, but far away from overflowing an int64_t */
#define SCALE_TO_U64_MAX (INT64_MAX / 4)
for (i = 0; i < n_entries; ++i)
total += entries[i].dbl;
scale_factor = SCALE_TO_U64_MAX / total;
for (i = 0; i < n_entries; ++i)
entries[i].u64 = tor_llround(entries[i].dbl * scale_factor);
if (total_out)
*total_out = (uint64_t) total;
#undef SCALE_TO_U64_MAX
}
/** Pick a random element of <b>n_entries</b>-element array <b>entries</b>,
* choosing each element with a probability proportional to its value, and
* return the index of that element. If all elements are 0, choose an index
* at random. If <b>total_out</b> is provided, set it to the sum of all
* elements in the array. Return -1 on error.
* choosing each element with a probability proportional to its (uint64_t)
* value, and return the index of that element. If all elements are 0, choose
* an index at random. Return -1 on error.
*/
/* private */ int
choose_array_element_by_weight(const uint64_t *entries, int n_entries,
uint64_t *total_out)
choose_array_element_by_weight(const u64_dbl_t *entries, int n_entries)
{
int i, i_chosen=-1, n_chosen=0;
uint64_t total_so_far = 0;
@ -1669,10 +1695,7 @@ choose_array_element_by_weight(const uint64_t *entries, int n_entries,
uint64_t total = 0;
for (i = 0; i < n_entries; ++i)
total += entries[i];
if (total_out)
*total_out = total;
total += entries[i].u64;
if (n_entries < 1)
return -1;
@ -1683,7 +1706,7 @@ choose_array_element_by_weight(const uint64_t *entries, int n_entries,
rand_val = crypto_rand_uint64(total);
for (i = 0; i < n_entries; ++i) {
total_so_far += entries[i];
total_so_far += entries[i].u64;
if (total_so_far > rand_val) {
i_chosen = i;
n_chosen++;
@ -1753,7 +1776,7 @@ smartlist_choose_node_by_bandwidth_weights(smartlist_t *sl,
double Wg = -1, Wm = -1, We = -1, Wd = -1;
double Wgb = -1, Wmb = -1, Web = -1, Wdb = -1;
uint64_t weighted_bw = 0;
uint64_t *bandwidths;
u64_dbl_t *bandwidths;
/* Can't choose exit and guard at same time */
tor_assert(rule == NO_WEIGHTING ||
@ -1834,7 +1857,7 @@ smartlist_choose_node_by_bandwidth_weights(smartlist_t *sl,
Web /= weight_scale;
Wdb /= weight_scale;
bandwidths = tor_malloc_zero(sizeof(uint64_t)*smartlist_len(sl));
bandwidths = tor_malloc_zero(sizeof(u64_dbl_t)*smartlist_len(sl));
// Cycle through smartlist and total the bandwidth.
SMARTLIST_FOREACH_BEGIN(sl, const node_t *, node) {
@ -1879,9 +1902,9 @@ smartlist_choose_node_by_bandwidth_weights(smartlist_t *sl,
if (weight < 0.0)
weight = 0.0;
bandwidths[node_sl_idx] = tor_llround(weight*this_bw + 0.5);
bandwidths[node_sl_idx].dbl = weight*this_bw + 0.5;
if (is_me)
sl_last_weighted_bw_of_me = bandwidths[node_sl_idx];
sl_last_weighted_bw_of_me = (uint64_t) bandwidths[node_sl_idx].dbl;
} SMARTLIST_FOREACH_END(node);
log_debug(LD_CIRC, "Choosing node for rule %s based on weights "
@ -1889,10 +1912,12 @@ smartlist_choose_node_by_bandwidth_weights(smartlist_t *sl,
bandwidth_weight_rule_to_string(rule),
Wg, Wm, We, Wd, U64_PRINTF_ARG(weighted_bw));
scale_array_elements_to_u64(bandwidths, smartlist_len(sl),
&sl_last_total_weighted_bw);
{
int idx = choose_array_element_by_weight(bandwidths,
smartlist_len(sl),
&sl_last_total_weighted_bw);
smartlist_len(sl));
tor_free(bandwidths);
return idx < 0 ? NULL : smartlist_get(sl, idx);
}
@ -1916,12 +1941,12 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
bandwidth_weight_rule_t rule)
{
unsigned int i;
uint64_t *bandwidths;
u64_dbl_t *bandwidths;
int is_exit;
int is_guard;
int is_fast;
uint64_t total_nonexit_bw = 0, total_exit_bw = 0;
uint64_t total_nonguard_bw = 0, total_guard_bw = 0;
double total_nonexit_bw = 0, total_exit_bw = 0;
double total_nonguard_bw = 0, total_guard_bw = 0;
double exit_weight;
double guard_weight;
int n_unknown = 0;
@ -1950,7 +1975,7 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
/* First count the total bandwidth weight, and make a list
* of each value. We use UINT64_MAX to indicate "unknown". */
bandwidths = tor_malloc_zero(sizeof(uint64_t)*smartlist_len(sl));
bandwidths = tor_malloc_zero(sizeof(u64_dbl_t)*smartlist_len(sl));
fast_bits = bitarray_init_zero(smartlist_len(sl));
exit_bits = bitarray_init_zero(smartlist_len(sl));
guard_bits = bitarray_init_zero(smartlist_len(sl));
@ -1986,7 +2011,7 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
bitarray_set(fast_bits, i);
if (is_known) {
bandwidths[i] = this_bw;
bandwidths[i].dbl = this_bw;
if (is_guard)
total_guard_bw += this_bw;
else
@ -1997,14 +2022,16 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
total_nonexit_bw += this_bw;
} else {
++n_unknown;
bandwidths[i] = UINT64_MAX;
bandwidths[i].dbl = -1.0;
}
} SMARTLIST_FOREACH_END(node);
#define EPSILON .1
/* Now, fill in the unknown values. */
if (n_unknown) {
int32_t avg_fast, avg_slow;
if (total_exit_bw+total_nonexit_bw) {
if (total_exit_bw+total_nonexit_bw < EPSILON) {
/* if there's some bandwidth, there's at least one known router,
* so no worries about div by 0 here */
int n_known = smartlist_len(sl)-n_unknown;
@ -2015,25 +2042,25 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
avg_slow = 20000;
}
for (i=0; i<(unsigned)smartlist_len(sl); ++i) {
if (bandwidths[i] != UINT64_MAX)
if (bandwidths[i].dbl >= 0.0)
continue;
is_fast = bitarray_is_set(fast_bits, i);
is_exit = bitarray_is_set(exit_bits, i);
is_guard = bitarray_is_set(guard_bits, i);
bandwidths[i] = is_fast ? avg_fast : avg_slow;
bandwidths[i].dbl = is_fast ? avg_fast : avg_slow;
if (is_exit)
total_exit_bw += bandwidths[i];
total_exit_bw += bandwidths[i].dbl;
else
total_nonexit_bw += bandwidths[i];
total_nonexit_bw += bandwidths[i].dbl;
if (is_guard)
total_guard_bw += bandwidths[i];
total_guard_bw += bandwidths[i].dbl;
else
total_nonguard_bw += bandwidths[i];
total_nonguard_bw += bandwidths[i].dbl;
}
}
/* If there's no bandwidth at all, pick at random. */
if (!(total_exit_bw+total_nonexit_bw)) {
if (total_exit_bw+total_nonexit_bw < EPSILON) {
tor_free(bandwidths);
tor_free(fast_bits);
tor_free(exit_bits);
@ -2050,12 +2077,12 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
* For detailed derivation of this formula, see
* http://archives.seul.org/or/dev/Jul-2007/msg00056.html
*/
if (rule == WEIGHT_FOR_EXIT || !total_exit_bw)
if (rule == WEIGHT_FOR_EXIT || total_exit_bw<EPSILON)
exit_weight = 1.0;
else
exit_weight = 1.0 - all_bw/(3.0*exit_bw);
if (rule == WEIGHT_FOR_GUARD || !total_guard_bw)
if (rule == WEIGHT_FOR_GUARD || total_guard_bw<EPSILON)
guard_weight = 1.0;
else
guard_weight = 1.0 - all_bw/(3.0*guard_bw);
@ -2068,19 +2095,19 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
sl_last_weighted_bw_of_me = 0;
for (i=0; i < (unsigned)smartlist_len(sl); i++) {
tor_assert(bandwidths[i] < UINT64_MAX);
tor_assert(bandwidths[i].dbl >= 0.0);
is_exit = bitarray_is_set(exit_bits, i);
is_guard = bitarray_is_set(guard_bits, i);
if (is_exit && is_guard)
bandwidths[i] = tor_llround(bandwidths[i] * exit_weight * guard_weight);
bandwidths[i].dbl *= exit_weight * guard_weight;
else if (is_guard)
bandwidths[i] = tor_llround(bandwidths[i] * guard_weight);
bandwidths[i].dbl *= guard_weight;
else if (is_exit)
bandwidths[i] = tor_llround(bandwidths[i] * exit_weight);
bandwidths[i].dbl *= exit_weight;
if (i == (unsigned) me_idx)
sl_last_weighted_bw_of_me = bandwidths[i];
sl_last_weighted_bw_of_me = (uint64_t) bandwidths[i].dbl;
}
}
@ -2099,10 +2126,12 @@ smartlist_choose_node_by_bandwidth(smartlist_t *sl,
guard_weight, (int)(rule == WEIGHT_FOR_GUARD));
#endif
scale_array_elements_to_u64(bandwidths, smartlist_len(sl),
&sl_last_total_weighted_bw);
{
int idx = choose_array_element_by_weight(bandwidths,
smartlist_len(sl),
&sl_last_total_weighted_bw);
smartlist_len(sl));
tor_free(bandwidths);
tor_free(fast_bits);
tor_free(exit_bits);

13
src/or/routerlist.h
View File

@ -217,8 +217,17 @@ int hex_digest_nickname_decode(const char *hexdigest,
char *nickname_out);
#ifdef ROUTERLIST_PRIVATE
int choose_array_element_by_weight(const uint64_t *entries, int n_entries,
uint64_t *total_out);
/** Helper type for choosing routers by bandwidth: contains a union of
* double and uint64_t. Before we call scale_array_elements_to_u64, it holds
* a double; after, it holds a uint64_t. */
typedef union u64_dbl_t {
uint64_t u64;
double dbl;
} u64_dbl_t;
int choose_array_element_by_weight(const u64_dbl_t *entries, int n_entries);
void scale_array_elements_to_u64(u64_dbl_t *entries, int n_entries,
uint64_t *total_out);
#endif
#endif

60
src/test/test_dir.c
View File

@ -4,6 +4,8 @@
/* See LICENSE for licensing information */
#include "orconfig.h"
#include <math.h>
#define DIRSERV_PRIVATE
#define DIRVOTE_PRIVATE
#define ROUTER_PRIVATE
@ -1382,12 +1384,51 @@ test_dir_v3_networkstatus(void)
ns_detached_signatures_free(dsig2);
}
static void
test_dir_scale_bw(void *testdata)
{
double v[8] = { 2.0/3,
7.0,
1.0,
3.0,
1.0/5,
1.0/7,
12.0,
24.0 };
u64_dbl_t vals[8];
uint64_t total;
int i;
(void) testdata;
for (i=0; i<8; ++i)
vals[i].dbl = v[i];
scale_array_elements_to_u64(vals, 8, &total);
tt_int_op((int)total, ==, 48);
total = 0;
for (i=0; i<8; ++i) {
total += vals[i].u64;
}
tt_assert(total >= (U64_LITERAL(1)<<60));
tt_assert(total <= (U64_LITERAL(1)<<62));
for (i=0; i<8; ++i) {
double ratio = ((double)vals[i].u64) / vals[2].u64;
tt_double_op(fabs(ratio - v[i]), <, .00001);
}
done:
;
}
static void
test_dir_random_weighted(void *testdata)
{
int histogram[10];
uint64_t vals[10] = {3,1,2,4,6,0,7,5,8,9}, total=0;
uint64_t zeros[5] = {0,0,0,0,0};
u64_dbl_t inp[10];
int i, choice;
const int n = 50000;
double max_sq_error;
@ -1396,13 +1437,13 @@ test_dir_random_weighted(void *testdata)
/* Try a ten-element array with values from 0 through 10. The values are
* in a scrambled order to make sure we don't depend on order. */
memset(histogram,0,sizeof(histogram));
for (i=0; i<10; ++i)
for (i=0; i<10; ++i) {
inp[i].u64 = vals[i];
total += vals[i];
}
tt_int_op(total, ==, 45);
for (i=0; i<n; ++i) {
uint64_t t;
choice = choose_array_element_by_weight(vals, 10, &t);
tt_int_op(t, ==, total);
choice = choose_array_element_by_weight(inp, 10);
tt_int_op(choice, >=, 0);
tt_int_op(choice, <, 10);
histogram[choice]++;
@ -1429,16 +1470,16 @@ test_dir_random_weighted(void *testdata)
/* Now try a singleton; do we choose it? */
for (i = 0; i < 100; ++i) {
choice = choose_array_element_by_weight(vals, 1, NULL);
choice = choose_array_element_by_weight(inp, 1);
tt_int_op(choice, ==, 0);
}
/* Now try an array of zeros. We should choose randomly. */
memset(histogram,0,sizeof(histogram));
for (i = 0; i < 5; ++i)
inp[i].u64 = 0;
for (i = 0; i < n; ++i) {
uint64_t t;
choice = choose_array_element_by_weight(zeros, 5, &t);
tt_int_op(t, ==, 0);
choice = choose_array_element_by_weight(inp, 5);
tt_int_op(choice, >=, 0);
tt_int_op(choice, <, 5);
histogram[choice]++;
@ -1477,6 +1518,7 @@ struct testcase_t dir_tests[] = {
DIR_LEGACY(param_voting),
DIR_LEGACY(v3_networkstatus),
DIR(random_weighted),
DIR(scale_bw),
END_OF_TESTCASES
};